This invention relates to a method of removing a soluble antimony compound from a liquid in which it is dissolved. In particular, it relates to the reaction of a hydrated compound, such as a hydrated carbonate or bicarbonate, with an antimony compound dissolved in a liquid to convert the soluble antimony compound into an antimony compound that is insoluble in the liquid.
Trifluoromethoxybenzene (TFMB) is an important commercial chemical intermediate used to make herbicides and other chemicals. It is typically made by reacting trichloromethoxybenzene (TCMB) with hydrogen fluoride, HF, at about 40 to about 45.degree. C. in the presence of antimony pentachloride, SbCl.sub.5, as a catalyst. The TFMB and the antimony pentachloride are miscible liquids and the antimony pentachloride dissolves in the TFMB. Some customers demand less than 5 ppm (parts per million, by weight) antimony in the TFMB product because antimony pentachloride is a Lewis acid and may catalyze side reactions in the next manufacturing step. Distilling the crude product in the presence of soluble antimony, however, may cause the decomposition of the product or further reactions of the product during distillation. Also, the presence of a metal, such as antimony, is not acceptable in chemicals used for electronic applications. Thus, to obtain an antimony-free product, it is necessary to either remove the soluble antimony catalyst prior to distillation or convert it to an insoluble form.
Antimony pentachloride can be removed from TFMB by heating it to a temperature of at least 140.degree. C., which results in the precipitation of antimony trichloride. This approach, however, may result in the decomposition of some of the TFMB or its loss with the chlorine gas byproduct.